A dry line TDR is used to locate anomalies on cabling used for networks,
PBX systems, and "in-house" wiring systems.

The Fluke DSP-100sr, DSP-2000, and DSP-41000 are the best units available and should
be used with either "smart remotes" or dual units back to back.

The DSP-100sr/2000/4000 will locate virtually any type of capacitively or inductively
isolated bug, high impedance device, or slave unit (if used properly).

The Microtest Pentascanner is an older unit, but performs well as a
backup unit.

Wet Line TDRs

A wet line TDR is used to locate anomalies on cabling used for
telephone and data communications with live voltages and
signals. This type of instrument is most useful when you can
only gain access to one end of the circuit.

The Riser-Bond 1200 series dual lead TDR is recommended for field usage and
tracing phone lines in an "outside-plant" environment.

Authors Rant About Proper TDR Usage

The Tektronix 1502 and 1503 TDR is an older style design, but
can be used to check wiring provided that there is no signal or
voltage present on the lines under test. The 1502 is a high
precision unit suitable for use on cable runs under a few
hundred feet, with the 1503 being a more general purpose unit
for longer cable runs.

Neither the 1502 or 1503 is appropriate for use on live telephone
lines, and you risk seriously damaging the instrument if subject
to such usage.

Not only will you NOT get a decent reading, you will screw up
the sensitivity on the sampler circuit, and you could blow out
the entire front end of your unit. While the damage may not show
up immediately, you are doing damage nonetheless.

The 1500 series is a DRY LINE TDR in that it can only be used
on a circuit that has less then five volts DC or AC on it. Because of
this they are far more sensitive then a wet line TDR (such as
the Riser Bond units).

If you need a dry line unit use a Fluke DSP or Tektronix unit,
but if you want a wet TDR for use on live lines use the Riser Bond
or similar unit. The 1500 series is STRICTLY a dry line TDR unless it has the
Ethernet option, and even then it is for WET ETHERNET, but DRY
"everything else".

This author would point out that VR3021 and VR3020 in the 1500 are 5.6
volt diodes on the front end, and that they will "go poof" if
you apply loop voltage for anything more then a few
milli-seconds. The A6 Ethernet Board bumps these voltages up a
bit, but it is still no where near the voltages found on normal
phone lines.

In the event that you are lucky enough to have the TDR connected
when ring voltage is applied you can expect to damage the unit
(which will permanently degrade performance, but may not totally
kill the unit).

The unit are designed to handle PERIODIC applications up to 400
volts, but it is ill-advised to every apply more then 11.2 volts
or you will get screwed up readings.

If you get into a pinch and have to use a 1500 series on a wet
line then add a cap in series to kill the DC, and a couple of
switching diodes to kill anything over 6 volts (and of course a
set of zener diodes). A small impedance matching circuit will also be
helpful.

Remember the 1500 was designed (many years ago) to test the
cabling on antenna's (involving a 300 mV signal), not telephone
loop circuits (with almost 50 volts).

The author uses and owns both the CRT and LCD versions of the
1502 and 1503, several Riser Bond units, 3-4 Flukes, and several
Microtest units along with several dual and quad lead ping
boxes.

Use the Tektronix 1502 for short DRY telephone lines, DRY coax,
HVAC wiring, intercom wiring, etc (this is perfect for things
that are less then 200 foot). The Tektronix 1503 is good for
long DRY telephone line, or for longer runs of DRY wire the 1502
can not develop enough voltage to ping.

For general purposes have several ping boxes you can use to
convert a hand-held O'scope into a TDR. These boxes are good
when you have to perform a TDR on live power lines, alarm lines,
HVAC wires, etc).

Let me say again... do not connect the 1502 or 1503 into a live
circuit.